Hard disk drives are used in many applications where relatively fast, economical, non-volatile mass storage is desired. For example, hard disk drives are commonly used in computer servers, mainframe computers, personal computers, laptop computers, digital video recorders, music and multimedia devices, personal digital assistants, digital cameras and cellular telephones, among other things. Hard disk technology has evolved significantly since the first commercial hard disk drive became available in 1956.
Present hard disk drives typically include a plurality of platters that spin at a constant angular velocity about a common rotational axis, or spindle. Common form factors, or platter diameters, of present generation hard disk drives are 3.5 in., 2.5 in., 1.8 in., 1 in. and 0.85 in. That said, other diameter platters are available. The platters are typically made of a non-metallic material, e.g., glass or aluminum, coated on both major surfaces with a magnetic recording material, typically iron oxide, that form the data storage surfaces of the drive. Present hard disk drives typically have a single armature that moves multiple read/write heads, one for each data storage surface, in unison with one another.
Several more recent designs utilize multiple read/write heads per data storage surface and move these multiple heads with corresponding respective independent armatures. In some of these designs, the multiple heads are used for redundancy or for increasing the speed of a given data transfer (read or write) operation by using some or all of the read/write heads simultaneously for that data transfer. In others of these designs, the multiple heads per data storage surface are controlled so that the read/write head closest to the location of the data at any given time is used for the data transfer. The one or more remaining read/write heads for that surface do not participate in that data transfer and await subsequent data transfer requests that call them into action. While these recent simultaneous read/simultaneous write and closest-to-the-data designs increase the speed of the respective hard disk drives, improvement in the average seek time, i.e., the average time it takes for the read/write head(s) to be moved to a desired data transfer location over a plurality of read/write requests, is highly desirable.